Dental attachment structure for the removable attachment and support for one of partial denture, an overdenture and bridge in the oral cavity is known to the prior art. Structures as represented generally by Letters U.S. Pat. Nos. 1,324,476 to S. G. Supplee, 1,664,726 to H. A. Adler and 3,787,975 to M. Zuest and others have been used for many years. With regard to the Supplee patent, there is the disclosure of a dental attachment structure including a post member and a sleeve member designed to be telescopically engaged with the post member. Supplee, also, describes a lining, received in position in the sleeve member by a cooperating dent and depression, which functions in the engagement of members in mounting a partial denture in the oral cavity. Engagement is solely through frictional contact between the lining and the post member.
The structure for attachment and support of a partial denture (as disclosed by Adler) essentially duplicates that structure described by Supplee. To this end, the Adler structure includes an independent metal leaf spring providing frictional retention of cooperating members which shall have been telescoped together. As is the case with the Supplee structure, retention of the partial denture described by Adler suffers from the problem of wear of the main components.
The Zuest patent discloses dental attachment structure for removable attachment and support of a partial or full denture in the oral cavity. The attachment structure includes an anchor formed with a socket at the base of a sleeve and a unit for support of the full or partial denture. The anchor is positioned within the root of a tooth which has been endodontically treated. The unit has structure which is attached to the framework of the full or partial denture and a spherically shaped head which is adapted for removable receipt in the socket. The anchor and/or unit are described of being formed of rubber, plastic or metal.
The Supplee, Adler and Zuest dental attachment structures are considered to suffer from various problems and disadvantages, the most important of which may be that of the requirement of repair or replacement of attachment structure in the event that contact surfaces are diagnosed as having become worn. Wear of contact surfaces results from the manner of attachment and support of the appliance within the oral cavity. To this end, the Supplee lining is described as being formed of metal, and most likely a hard metal, to provide the characteristic of elasticity or spring required for retention. Repeated insertion and removal of the appliance results in wear of the post member which ultimately will require repair or reconstruction. The Supplee device is considered to suffer from a further problem, namely a problem that develops from a required shortening of the post member to facilitate mounting to the abutment tooth which may also be short. A shortening of the post member and consequently the sleeve member reduces the area of contact between the lining and the post member, and frictional retention will be limited.
The problem of wear of contact surfaces is considered compounded in the dental attachment structure of Zuest. To this end, Zuest, unlike Supplee and Adler, employs no lining or similar structure so that wear of surface may be diagnosed on either or both of the anchor and unit. Thus, the diagnosis may be such to require replacement of the entire component.
The prior art also includes a form of extracoronal attachment sold by APM-Sterngold of San Mateo, California under the name "Hader Vertical Extension". The Hader extracoronal attachment includes a male member and a female member, and, in use, the male member of a plastic material is cast in metal on the outside of the crown contour of an abutment tooth. The female member is incorporated in an acrylic resin within a hollowed-out plastic tooth of a partial denture. Just as wear of contact surfaces became a problem with the previously referred to prior art dental attachment structures, that problem as well as a problem relating to the strength characteristic of the plastic male member is a problem in Hader structure. A further problem or disadvantage resides in the external placement of the male member of the Hader structure